Observation of a Lymphatic Pump in a Human by Using Photoacoustic Imaging

Abstract

Supplemental Digital Content is available in the text.

Sir,

Although lymph vessels are one of the most important systems in the human body, it is difficult to observe them because their diameter is small and the lymph fluid is transparent. PAI-05¹ is the new photoacoustic imaging device that can facilitate observation of the lymphatic vessels at a 0.2-mm resolution. Previously, we reported the results of the observation of the lymphatic system using photoacoustic imaging.^2–4 Additionally, this device can also record a video as the sensor can be fixed.⁵ We obtained the lymphatic flow video of the following case.

CASE

A 62-year-old woman presented with primary lymphedema tarda (Fig. 1A). Lymphoscintigraphy revealed dermal backflow in her lower leg, and this finding led to the diagnosis. After injecting indocyanine green on her first and fourth web, photoacoustic imaging was started; it revealed the lymphatic vessels clearly with subcutaneous veins. The lymphatic vessels had separated into 2 branches at a slightly deeper level in the dermal backflow of the lateral aspect of the lower extremity (Fig. 1B). By taking the video just before the dermal backflow, it was noted that the lymphatic flow was intermittent and not continuous, and the lymphatic flow was observed twice during the 5-minute imaging procedure. (See figure, Supplemental Digital Content, which is a continuous photograph of the lymphatic flow. The lymph does not always flow but streams every few minutes, http://links.lww.com/PRSGO/B409.) (See Video 1 [online], which shows how the lymphatic flow was observed twice during the 5-minute imaging procedure. The velocity of the lymphatic flow was 0.83–1 mm/s.) The velocity of the lymphatic flow was 0.83–1 mm/s, as noted by using frame advance (see Video 1 [online], which shows how the lymphatic flow was observed twice during the 5-minute imaging procedure. The velocity of the lymphatic flow was 0.83–1 mm/s).

Fig. 1.

Photographs of a 62-year-old woman with primary lymphedema tarda. A, Left lower extremity of the patient. B, A photoacoustic lymphangiographic image of the left lateral lower extremity taken after a subcutaneous injection of 0.5 mL of indocyanine green showing dilated dermal lymphatics (yellow) and superficial veins (blue). We checked the flow at the point indicated by a circle.

Video 1. Video 1 from “Observation of a Lymphatic Pump in a Human by Using Photoacoustic Imaging”.

Download video file ^{(27MB, mp4)}

It is known that lymphatic fluid is pumped from the lymphatic vessels owing to the activity of the surrounding smooth muscles. However, it has been difficult to observe the lymphatic flow in the a live human body using previous modalities. The lymphatic fluid does not flow continuously but intermittently owing to spontaneous smooth muscle contraction. This phenomenon is known as a lymphatic pump, and this has never been visualized.

By observing the lymphatic vessel directly, we can check the velocity of the lymphatic fluid. Previously, velocity of the lymphatic fluid was calculated indirectly, and the data showed a lot of variation. However, this photoacoustic technique, which is associated with a high resolution quality, could help the progress of lymphatic research.

DISCLOSURE

Dr. Aiso is the CEO of Luxonus Inc, the developing company of the photoacoustic imaging system discussed in this article. The other authors have no financial interest to declare. This research was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).

ACKNOWLEDGMENT

This research was done in accordance with the ethical standards of the ethics committee at Keio University Hospital and Certified Review Board of Keio and with the Helsinki Declaration of 1975, as revised in 1983.